Process for manufacturing glass optical elements

ABSTRACT

Disclosed are processes for manufacturing glass optical elements by press molding a heated and softened glass material in preheated molds. In the process, the glass material is heated while it is floated by a gas blow and the heated and softened glass material is transferred to the preheated molds and then subjected to press molding. Alternatively, the process comprises: heating a glass material at a temperature at which the glass material has a viscosity of lower than 10 9  poises, preheating molds at a temperature at which the glass material has a viscosity of from 10 9  to 10 12  poises, subjecting the heated and softened glass material to initial press in the preheated molds for 3 to 60 seconds, starting to cool the vicinity of molding surfaces of the molds at a rate of 20° C./minute or higher upon starting of, or during, or after the initial press, and removing a molded glass article from the molds after the temperature of the vicinity of the molding surfaces of the molds becomes a temperature equal to or lower than a temperature at which the glass material has a viscosity of 10 12  poises.

This application is a divisional of application Ser. No. 09/432,388,filed on Nov. 2, 1999, now U.S. Pat. No. 6,564,584, which in turn is adivisional of Ser. No. 09/244,174, filed on Feb. 4, 1999, now U.S. Pat.No. 6,009,725, which in turn is a divisional of Ser. No. 08/881,751,filed on Jun. 24, 1997, U.S. Pat. No. 5,873,921; which in turn is acontinuation of Ser. No. 08/526,702, filed on Sep. 11, 1995, nowabandoned.

BACKGROUND OF THE INVENTION

The present invention relates to a process for manufacturing glassoptical elements such as glass lenses, which require no grinding andpolishing after their press molding. In particular, the presentinvention relates to a process for manufacturing glass optical elements,which can improve production speed by markedly shortening the cycle timerequired for the press molding.

There have been known various processes for manufacturing glass opticalelements, which require no grinding and polishing after their pressmolding, by molding glass preforms, which are glass materials to befurther molded, in molds which ensure surface accuracy and surfaceroughness required for surfaces of molded glass articles.

For example, Japanese Patent Un-examined Publication (KOKAI, hereinafterreferred to as “JP-A”) No. 64-72929 and Japanese Patent Publication(KOKOKU, hereinafter referred to as “JP-B”) No. 2-16251 discloseprocesses where molds and glass preforms are heated together. In thesemethods, a glass preform is inserted into a mold assembly comprising anupper mold, a lower mold and a guide mold which guides the upper moldand the lower mold, and the preform is heated together with the moldassembly to a temperature where the preform is softened sufficiently andthen the preform is subjected to press molding. Then, they are cooled atsuch a cooling rate that surface accuracy of the glass article aftermolding is not deteriorated to a temperature around the glass transitiontemperature, or allowed to cool to room temperature with a certainperiod of time, and the molded glass article is removed from the moldassembly.

JP-A-62-113730 and JP-B-63-46010 disclose processes where apreliminarily softened glass preform is inserted into a separatelyheated mold assembly. In these methods, a glass preform placed on aring-like member is softened by heating it together with the ring-likemember, inserted into a mold assembly with the ring-like member andpress molded between an upper mold and a lower mold which penetrates thering-like member and lifts up the softened preform. Alternatively, thering-like member acts as a guide mold guiding the upper mold and thelower mold to perform the press molding. JP-A-61-251529, JP-A-61-286232,JP-A-62-27334 and JP-A-63-45134 also disclose processes for moldingglass optical elements where a preliminarily softened glass preform isinserted into a separately heated mold assembly. However, theseprocesses have drawbacks that they occasionally cannot mold a desiredshape when relatively large deformation of the glass material isrequired, and that they are likely to generate sink marks and distortionand thus difficult to obtain sufficient surface accuracy.

JP-A-62-27334 discloses a process where a glass preform is inserted intoa mold assembly by using a ring-like member and molded, as well astemperature conditions for prolonging the lifetime of molds for such aprocess. In this method, the mold temperature is maintained within atemperature range of from a temperature just below the glass transitionpoint to a temperature lower than the glass transition point by 200° C.,and a glass preform, which has been preliminarily heated to such atemperature that the preform had a viscosity ranging from 10⁶ to 10⁸poises, is inserted into the mold assembly and press molded.

In the above-mentioned processes where a preform is heated, molded andcooled with molds while the preform is maintained in a mold assembly,the temperatures of the glass and the molds are approximately the samethroughout the molding process and hence there would be no temperaturedifference between the surface and the inside of the glass. Therefore,sink marks are prevented and thereby high surface accuracy is provided.However, since it requires a temperature elevating period before thepressing and a cooling period after the pressing and before theejection, it has a drawback of extremely long cycle time required forthe whole process. In addition, since the glass is contacted with moldsurfaces for a long period of time during the heating and the pressing,it has also a drawback that the glass is likely to react with the moldsurfaces and thereby the lifetime of the molds is shortened.

On the other hand, in the process where a glass preform which ispreliminarily heated to have a higher temperature (low viscosity) thanmolds is inserted into the molds by using a ring-like member and pressmolded, press time may be very short. In addition, since the moldtemperature may be relatively low and release of a molded glass frommolds is possible after a relatively short period of time to allow themolded glass to cool after the pressing, the cycle time can be markedlyshortened. However, if the preform is inserted into the molds at a lowtemperature (within a temperature range of from a temperature just belowthe glass transition point to a temperature lower than the glasstransition point by 200° C.) to prolong the lifetime of the molds, thetemperature of the glass surface is rapidly lowered and the glass iscooled and solidified before it is press molded to a desired thickness.Therefore, it has drawbacks that it cannot stably provide moldedarticles, especially glass molded articles with a small edge thickness(about 1.0 to 1.3 mm) such as biconvex lenses and meniscus lenses, andthat it shows insufficient surface accuracy.

To solve the above-described problems, it has been proposed to use aglass preform showing a further lower viscosity under similartemperature conditions of molds. However, as the viscosity becomeslower, the softened preform on the ring-like member becomes more likelyto sag at the opening of the ring member (deformed and hanged down). Forexample, though it depends on the shape of the preform, when theviscosity is 10⁷ poises or lower, the preform is very likely to sag.Therefore, to prevent deformed preform from dropping down from thering-like member, it is necessary to use a glass preform having an outerdiameter quite larger than the inner diameter of the preform supportingportion of the ring-like member.

As a result of it, press molded lenses have a quite larger outerdiameter than desired and hence it is necessary to cut off a largesurplus in a post-processing so that they have a desired outer diameter.Further, in this method using a ring-like member, since molding flash isproduced due to the use of a preform larger than the final product andthe generation of surplus and, since a low mold temperature is used, itis very difficult to produce biconvex lenses, meniscus lenses and thelike with a small edge thickness.

Therefore, one of the objects of the present invention is to provide aprocess for manufacturing glass optical elements by press molding aheated and softened glass material such as a glass preform in preheatedmolds, wherein the glass material is easily held during its heating andsoftening even if a glass material such as a glass preform of whichviscosity is decreased when it is softened and hence which is likely todeform is used and thus a glass optical element can be produced.

A further object of the present invention is to provide a processcapable of satisfactorily, manufacturing glass optical elements bytransferring a heated and softened glass preform and the like, which isprone to be deformed, to molds without unduly deforming it.

A further object of the present invention is to provide a process formanufacturing glass optical elements, which uses a glass material suchas a glass preform which enables to provide a molded glass with a sizeapproximately the same with an effective outer diameter desired for apurpose glass optical element and therefore can minimize an edgingvolume for centering in a post-processing.

A further object of the present invention is to provide a process formanufacturing glass molded articles of which cycle time required forpress molding is remarkably shortened and which can provide glass moldedarticles with no surface defects and with high surface accuracy.

An additional object of the present invention is to provide a processcapable of easily manufacturing biconvex lenses, meniscus lenses and thelike with a small edge thickness.

A still further object of the present invention is to provide a processcapable of transferring a heated and softened glass gob, which is proneto be deformed, to molds to satisfactorily manufacture glass opticalelements.

One of the objects of the present invention is to provide a process formanufacturing glass optical elements by press molding a heated andsoftened glass material such as a glass preform in a preheated molds,which can remarkably shorten the cycle time required for the pressmolding, stably provide lenses and the like even though they must have asmall edge thickness and show good surface accuracy.

A further object of the present invention is to provide a process formanufacturing glass optical elements without sink marks and distortionand with high surface accuracy.

A further object of the present invention is to provide a processcapable of manufacturing glass optical elements without sink marks anddistortion and with high surface accuracy and a center thickness withinan allowance.

SUMMARY OF THE INVENTION

The present invention provides, as a first aspect of the invention, aprocess for manufacturing glass optical elements by press molding aheated and softened glass material in preheated molds, wherein the glassmaterial is heated while it is floated by a gas blow and the heated andsoftened glass material is transferred to the preheated molds and thensubjected to press molding.

In one embodiment of the above-described process, the heated andsoftened glass material is transferred to the preheated molds bydropping the material.

In another embodiment of the above-described process, a heated andsoftened glass material is transferred to the preheated molds by holdingthe glass material by suction or placing it on a ring-like member havingan inner diameter smaller than the outer diameter of the glass materialand subjected to press molding.

In another embodiment of the above-described process, a heated andsoftened glass material is transferred to the preheated molds bysplitting a floating means used for heating the glass material into twoor more pieces and removing the pieces to drop the glass material andthe glass material is subjected to press molding.

The present invention further provides, as a second aspect of theinvention, a process for manufacturing glass optical elements by pressmolding a heated and softened glass material in preheated molds, whichcomprises:

heating a glass material at a temperature at which the glass materialhas a viscosity of lower than 10⁹ poises,

preheating molds at a temperature at which the glass material has aviscosity of from 10⁹ to 10¹² poises,

subjecting the heated and softened glass material to initial press inthe preheated molds for 3 to 60 seconds,

starting to cool the vicinity of molding surfaces of the molds at a rateof 20° C./minute or higher upon starting of, or during, or after theinitial press, and

removing a molded glass article from the molds after the temperature ofthe vicinity of the molding surfaces of the molds becomes a temperatureequal to or lower than a temperature at which the glass material has aviscosity of 10¹² poises.

In one embodiment of the second aspect of the present inventiondescribed above, the molding surfaces of the molds have an amorphousand/or crystalline carbon mono-component or mixture layer of graphitestructure and/or diamond structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory schematic view of press molding in a moldassembly used in the present invention.

FIG. 2 is an explanatory schematic view of the method for softening afloating glass preform above a floating means and transferring thepreform according to the present invention.

FIG. 3 is an explanatory schematic view of the method for softening afloating glass material above a floating means according to the presentinvention.

FIG. 4 is an explanatory schematic view of the method for softening afloating glass preform above a floating means according to the presentinvention.

FIG. 5 is an explanatory schematic view of the method for softening afloating glass preform above a floating means according to the presentinvention.

FIG. 6 is an explanatory schematic view of the method for transferring asoftened glass preform to molds according to the present invention.

FIG. 7 is an explanatory schematic view of the method for transferring aglass preform softened above a floating means to molds by suckingaccording to the present invention.

FIG. 8 is an explanatory schematic view of the method for transferring aglass preform softened above a floating means to the molds by suckingaccording to the present invention.

FIG. 9 is an explanatory schematic view of the press molding in a moldassembly used in the present invention.

FIG. 10 is an explanatory schematic view of the method for transferringa softened glass preform to molds according to the present invention.

FIG. 11 is an explanatory schematic view of the method for transferringa softened glass preform to molds according to the present invention.

FIG. 12 is an explanatory schematic view of the method for transferringa softened glass preform to molds according to the present invention.

FIG. 13 is an explanatory schematic view of the method for transferringa softened glass preform to molds according to the present invention.

FIG. 14 is an explanatory schematic view of the method for transferringa softened glass preform to molds according to the present invention.

FIG. 15 is an explanatory schematic view of the method for transferringa softened glass preform to molds according to the present invention.

FIG. 16 is an explanatory schematic view of the press molding in a moldassembly used in the present invention.

FIG. 17 is an explanatory schematic view of a lower mold of a moldassembly used in the Examples.

FIG. 18 is an explanatory schematic view of press molding in a moldassembly used in the Examples.

FIG. 19 is an explanatory schematic view of press molding in a moldassembly used in the Examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Aspect of the Invention

The process according to the first aspect of the present invention is aprocess for manufacturing glass optical elements by press molding aheated and softened glass material to be molded in preheated molds.

Types, shapes and the like of the glass materials used for the presentinvention may be conventional ones. However, the glass materials usedfor the present invention are preferably utilized at a relatively lowviscosity. For example, heated and softened glass materials preferablyhas a viscosity of from 10^(5.5) to 10^(9.0) poises.

The glass materials may be in the form of, for example, a glass preformor glass gob. Glass preform is a term to refer to a molded articlehaving a desired shape to be used as a precursor for manufacturing glassoptical elements. The glass preforms may be those obtained by coldforming or hot forming of molten glass and may be such preforms furthersubjected to mirror polishing and the like. Further, the preforms mayhave rough surfaces, rather than mirror surfaces, and, for example, maybe ground articles ground with #800 diamond.

The shape of the glass preforms is decided considering sizes, volumes ofproducts, i.e., glass optical elements, their volume changes uponmolding and the like. Further, in order to prevent formation of gastraps upon molding, it is preferred that glass preforms have such ashape that centers of molds initially contact with surfaces of thepreforms to be molded. For example, glass preforms may be spheres, orhave marble-like, disc-like shapes, or shapes having spherical surfacesand the like.

Glass gobs are glass pieces obtained by splitting molten glass into adesired volume and they usually have irregular chill marks. Examples ofthe above-described glass preforms are obtained by molding these glassgobs into a desired shape. Glass gobs are softened by heating while theyare floated, and they may be heated so that they have a glass viscosityof 10⁵ poises or lower to eliminate wrinkles (chill marks) on theirsurfaces.

Volumes of glass preforms or gobs may be slightly larger than those offinal products and, in such a case, final outer diameters can beobtained by subjecting the molded articles to edging in post-processing.

For the present invention, mold structure may have a structure wherepressure is applied to molded articles (optical elements) during coolingafter molding, or a structure where pressure can be reduced afterinitial press. Further, they may have a structure where pressure isapplied by weight of upper molds after the initial press. Molds can beheated by resistance heaters, high-frequency heaters, infrared lampheaters and the like. In particular, high-frequency heaters and infraredlamp heaters are preferred, since they can recover mold temperature in ashort period of time. Cooling of molds can be performed by electric cutcooling, cooling gas passing through inside of molds and the like.

The molds used for the present invention may be, for example, a moldassembly 39 comprising an upper mold 35, a lower mold 34 and a guidemold 36 as shown in FIG. 1. However, molds are not limited to it. Themolds may be those obtained by forming a silicon carbide layer on asilicon carbide sintered body by a CVD technique and forming thereon ani-carbon (diamond-like carbon) layer by an ion-plating technique. Alsoused are those composed of silicon, silicon nitride, tungsten carbide orcermets of aluminum oxide-base and cermets of titanium carbide-base andsuch materials of which surfaces are preferably further coated withdiamond, heat resistant metals, noble metal alloys, ceramics ofcarbides, nitrides, borides, oxides and the like. Those having carboncoatings such as i-carbon coatings are particularly preferred, becausethey show excellent releasability.

Conditions for press molding may be suitably selected depending ontemperatures (viscosities) of glass materials such as preforms and gobsand temperatures of molds and the like. Normally, molding is performedby pressing at a pressure of from 30 to 300 kg/cm² for 3 to 60 seconds,preferably 5 to 30 seconds. Temperature of glass materials, moldtemperature and mold release temperature may also be optionallyselected.

The manufacturing process according to the first aspect of the presentinvention is characterized in that preheating of a glass material iscarried out by heating the glass material while it is floated by a gasblow and the heated and softened glass material is transferred to thepreheated molds.

In a viscosity range where the glass materials are deformed by their ownweight, it is not easy to prevent adhesion between the glass materialsand the means for supporting the glass materials upon heating. Accordingto the present invention, the glass materials are floated by a gas blow,for example, by blowing gas from inside of the supporting means. As aresult, gas layers are formed on both surfaces of the means and theglass materials and it is made possible to heat and soften the glassmaterials while obviating any reaction between the supporting means andthe glass materials. Further, when the glass material is a glasspreform, the glass preform may be heated and softened while the shape ofthe preform is substantially maintained. When the glass material is aglass gob, it is possible to deform the gob to obtain its appropriateshape and eliminate its surface defects by heating and softening itwhile it is floated by a gas blow even if the glass gob has had anirregular shape and surface defects such as wrinkles.

Gas for the gas blow used for floating the glass materials in thepresent invention is not particularly limited. However, it is preferablya non-oxidative gas such as nitrogen, since the heated glass materialshould not react with the supporting means and deterioration of thesupporting means by oxidation should be prevented. Reducing gas such ashydrogen gas may be added to the gas.

Flow rate of the gas may be suitably selected depending on shapes of anoutlet for the gas blow, shapes and weights of the glass materials andthe like. Normally, a flow rate ranging from 0.005 to 20 liters/minuteis suitable for floating the glass materials. When the flow rate islower than 0.005 liters/minute, it may sometimes be impossible tosatisfactorily float the glass materials. When the flow rate exceeds 20liters/minute, the glass material above the supporting means is undulyswayed and, when the glass material is a glass preform, it may bedeformed upon heating even though it has a weight of not less than 2000mg.

Conditions for heating and softening the glass materials may be suitablyselected depending on types of the glass materials and the like andadjusted so that softened glass materials have a desired viscosity.

The glass materials can be floated by a gas blow which is blown offupward from an upper opening having an opening diameter smaller than adiameter of the glass materials. As shown in FIG. 2, an upper opening 11of a floating means 10 has a diameter smaller than that of a glassmaterial 1, and the glass material 1 is floated and maintained above theupper opening 11 by a gas blow blowing off upward from the bottom 12 ofthe upper opening 11 of the floating means 10 so that the material isnot contacted with the floating means 10. The floating means 10 may be,as shown in FIG. 3, composed of separable two portions 10 a and 10 b.The glass material 1 is heated by surrounding heaters for softeningglass 14.

The glass materials may be, whether they may be a glass preform or gob,floated by a gas blow as shown in FIG. 3.

The glass materials may also be floated by a gas blow blowing off from aspherically hollowed surface of a porous material having a curvaturesimilar to that of the shape of glass material or a flat surface of aporous material. In particular, when the glass material is a glasspreform, it is effective since it makes it very easy to maintain theshape of the preform. When the glass material is a glass gob, it is alsopossible to easily eliminate surface defects of the glass gob by heatingit while it is floated by a gas blow from a porous surface.

As shown in FIG. 4, the glass material 1 is maintained in a floatingstate by a gas blow blowing off from the porous surface 18 above thefloating means 17, which is supported by a floating means support 19 andhas a spherical porous surface 18 of which curvature is similar to thatof the glass material 1. The floating means support 19 and the floatingmeans 17 may have, like in FIG. 3, a split structure. The glass material1 is heated by the surrounding heaters for softening glass 14.

The heating of the glass materials includes heating the materials of anambient temperature to a desired temperature, or heating the material ofa somewhat elevated temperature to a desired temperature. In addition, aglass material already heated to a desired temperature may also be used.For example, when the glass material is a glass gob, a glass gob made ofmolten glass may be used without cooling it.

Therefore, the present invention encompasses a process for manufacturingglass optical elements by press molding a heated and softened glassmaterial in preheated molds, wherein the glass material is a softenedglass gob which is obtained by taking a portion of molten glass and theglass gob is floated by a gas blow to eliminate surface defects of theglass gob, then transferred to the preheated molds and press molded.

To obtain a glass gob by taking a portion from molten glass, anyconventional method can be used. For example, a softened glass gob witha desired volume can be obtained by cutting off a glass piece frommolten glass melted at a desired temperature. Elimination of surfacedefects of glass gobs can be efficiently performed by floating the glassgobs having a viscosity of not more than 10⁵ poises by a gas blow.

When the glass material is a glass preform, it may first be heated to atemperature lower than its glass transition temperature by 30° C. ormore and then further heated to a desired temperature while it isfloated by a gas blow. Such a process is shown in FIG. 5. As shown inFIG. 5, the glass material 1 is heated on a means for supporting glassmaterial 20 to a temperature lower than the glass transition temperatureby 30° C. or more. Then, the heated glass material 1 is transferred tosuch a floating means as shown in FIG. 2 or 3 by means of an appropriatetransfer means. In FIG. 5, exemplified is transfer of glass material 1to a floating means 10 by means of a movable suction holding means 15having a lower opening. For the transfer of the heated glass material 1,any means other than the above-described suction holding means, such asa ring-like member on which a glass material is placed may also be used.

In one embodiment, a heated and softened preform may be transferred topreheated molds by holding the preform by suction. For example, suchtransfer may be performed by the movable suction holding means 15 havinga lower opening 16 shown in FIG. 2. The lower opening 16 is connected toa means for internally sucking such as reduced pressure pumps and vacuumpumps and the lower opening 16 is capable of holding a glass preform bysuction. A glass preform 1 heated and softened above the floating means10 is held at the lower opening 16 of the movable holding means 15 bysuction and transferred to a position over the molding surface 40 of thelower mold 34 as shown in FIG. 6. Then, the softened preform 1 is pressmolded by the molding surface 40 of the lower mold 34 and the moldingsurface 41 of the upper mold 35 as shown in FIG. 1 to give an glassoptical element 2.

The heated and softened preform may also be held by suction by suckingfrom suction holes provided in the vicinity of the molding surface ofthe upper mold. For example, it may be held by sucking from the suctionholes 45 provided on the guide mold 36 disposed in the vicinity of themolding surface 41 of the upper mold 35 shown in FIG. 7. As shown inFIG. 7, the softened preform 1 above the floating means 10 istransferred to a position near the lower opening of the guide mold 36provided together with the upper mold 35, and then, as shown in FIG. 8,the preform 1 is lifted and stuck to the molding surface 41 by suckingfrom the suction holes 45 of the guide mold 36. Then, the floating means10 is removed, a lower mold is transferred to a position under thesoftened preform or the softened preform held by suction at the vicinityof the molding surface of the upper mold is transferred to a positionover a molding surface of the lower mold, and the preform may be pressmolded by the molding surfaces of the upper mold and the lower mold(FIG. 9).

Transfer of a heated and softened preform to preheated molds may also beperformed by placing the preform on a ring-like member having an innerdiameter smaller than the outer diameter of the preform and holding bysuction the member on which the preform is placed.

For example, as shown in FIG. 10, a ring-like member 23 having an innerdiameter slightly larger than the outer diameter of the upper opening ofthe floating means 10 and smaller than the outer diameter of the preform1 is placed so that the upper opening of the floating means 10 ispositioned within the ring of the ring-like member 23. After the preformis softened to a desired viscosity, the preform heated and softenedwhile floating above the floating means 10 is placed on the ring-likemember 23 and transferred. For the transfer of the ring-like member 23,vacuum pad 24 capable of holding the ring-like member 23 by suction isexemplified in FIG. 10. However, means for transferring the ring-likemember is not particularly limited.

Then, as shown in FIG. 11, the preform 1 is transferred to a positionover the molding surface 40 of the lower mold 34 on which the preform 1is to be placed, and the suction of vacuum pad 24 is stopped to placethe preform 1 on the molding surface 40. The preform 1 on the moldingsurface 40 is press molded between the upper and lower molds as shown inFIG. 1.

In another embodiment according to the first aspect of the presentinvention, the transfer of the heated and softened glass material isperformed by dropping the softened glass material. The heated andsoftened glass material may be dropped, for example, by splitting afloating means into two or more pieces and removed the pieces to make anopening under the material. For example, as shown in FIG. 12, the glassmaterial 1 is softened by heating above the floating means 10 and thenthe glass material 1 is dropped since the floating means 10 ishorizontally separated into two parts, 10 a and 10 b, and moved toopposite directions (right and left in the figures) as shown in FIG. 13.The lower mold 34 is provided as a receiver of the dropped glassmaterial 1 and thus the glass material 1 is transferred onto the moldingsurface 40 of the lower mold 34 in a moment.

Further, in the above-described embodiment, a guide means may beutilized to drop and transfer the heated and softened glass materialonto the center position of the molding surface without any deviation.For example, as shown in FIGS. 12 and 13, the cylindrical guide means 50having an inner diameter capable of providing an appropriate clearanceagainst the maximum outer diameter of the glass material 1, which iscomposed of separable portions 50 a and 50 b,is provided above thefloating means 10, and thus the glass material can be dropped onto thecenter of the mold. Structure and the like of the guide means would notbe particularly limited, so long as it can prevent deviation of theglass material upon split and removal of the floating means. Forexample, the guide means may be composed of, not a cylinder, but aplurality of pipes arranged as a grille, or two or more facing panels.The guide means may have a structure which can be removed as two or moreportions. Further, the guide means may be provided under the floatingmeans.

Structure for separating and removing the floating means used forheating the glass material is not particularly limited. For example,when the floating means is moved horizontally as described above, thefloating means may be separated into three or four portions and therespective portions may be removed along three directions (adjacentdirections are different by 120°) or four directions (adjacentdirections are different by 90°) respectively to drop the glassmaterial.

Further, the floating means may also be composed of floating meansportions 17 a and 17 b, which have pivot shafts 18 a and 18 brespectively, as shown in FIG. 14. The floating means portions 17 a and17 b can move downward by pivoting around the shafts 18 a and 18 b and,as a result of such pivoting movements, the floating means can opendownward to drop the glass material 1. Further, as shown in FIG. 15, thefloating means may also be composed of floating means portions 19 a and19 b, which have pivot shafts 18 a and 18 b respectively. The floatingmeans portions 19 a and 19 b can move downward by pivoting around theshafts 18 a and 18 b and, as a result of such pivoting movements, thefloating means can open downward to drop the glass material 1.

In the embodiment of the present invention described above, the heatedand softened glass material can be transferred into the molds in amoment by dropping the glass material.

Though the above-described embodiment has been explained by referring tosoftening and molding of glass preforms, glass optical elements can bemanufactured by heating, transferring and molding glass materials otherthan glass preforms, for example, glass gobs.

Second Aspect of the Invention

The process according to the second aspect of the present invention is aprocess for manufacturing glass optical elements by press molding heatedand softened glass material in preheated molds, which comprises:

heating a glass material at a temperature at which the glass materialhas a viscosity of lower than 10⁹ poises,

preheating molds at a temperature at which the glass material has aviscosity of from 10⁹ to 10¹² poises,

subjecting the heated and softened glass material to initial press inthe preheated molds for 3 to 60 seconds,

cooling the vicinity of molding surfaces of the molds at a rate of 20°C./minute or more, and

removing a molded glass article from the molds after the temperature ofthe vicinity of the molding surfaces of the mold becomes a temperatureequal to or lower than a temperature at which the glass material has aviscosity of 10¹² poises.

In one embodiment of the second aspect of the present inventiondescribed above, the molding surfaces of the molds have an amorphousand/or crystalline carbon mono-component or mixture layer of graphitestructure and/or diamond structure.

Types, shapes and the like of glass materials used in the processaccording to the second aspect of the present invention may be similarto those used for the process according to the first aspect of thepresent invention.

In this molding process of the present invention, the glass material issoftened by heating it to a temperature at which the glass material hasa viscosity of lower than 10⁹ poises. Because of the viscosity of theglass material lower than 10⁹ poises, the glass material can besufficiently deformed and molded in the molds preheated to a temperatureat which the glass material has a viscosity not less than 10⁹ poises. Tocarry out the molding with a relatively low mold temperature, it ispreferred that the glass material is softened by heating it to atemperature at which the glass material has a viscosity of from 10^(5.5)to 10^(7.4) poises.

The molds are preheated at a temperature at which the glass material hasa viscosity of from 10⁹ to 10¹² poises. At a temperature lower than atemperature at which the glass material has a viscosity of 10¹² poises,it is difficult to sufficiently extend the glass material to obtainglass molded articles having a thin edge thickness, and it is alsodifficult to obtain high surface accuracy. At a temperature of moldshigher than a temperature at which the glass material has a viscosity of10⁹ poises, molding cycle time is unduly prolonged and mold lifetime isshortened.

Conventional molds can be used for the present invention as they are.However, those of which molding surfaces have an amorphous and/orcrystalline carbon mono-component or mixture layer of graphite structureand/or diamond structure are preferred. In the molds having such carbonlayers as described above, adhesion of glass would not occur even thoughthe mold temperature is higher than the glass transition point of theglass material.

The carbon layers described above can be formed by spatteringtechniques, plasma CVD techniques, CVD techniques, ion platingtechniques and the like. When the layers are formed by a spatteringtechnique, spattering is preferably carried out by using a substratetemperature of 250 to 600° C., RF power density of 5 to 15 W/cm², degreeof vacuum during spattering of 5×10⁻⁴ to 5×10⁻¹ torr as well as an inertgas such as Ar as spattering gas and graphite as a spattering target.

When the layers are formed by a microwave plasma CVD technique, they arepreferably formed under conditions of a substrate temperature of 650 to1000° C., microwave power of 200 W to 1 kW, gas pressure of 10⁻² to 600torr by using methane and hydrogen gases as raw material gases.

When the layers are formed by an ion plating technique, they arepreferably formed by using a substrate temperature of 200 to 450° C. andionizing benzene gas.

The carbon layers include those with and without C—H bonds.

In this press molding process of the present invention, the heated andsoftened glass material is subjected to initial press in the preheatedmolds for 3 to 60 seconds. When the initial press is shorter than 3seconds, extension of the glass would be insufficient and hence glassoptical elements of desired shapes cannot be obtained. On the otherhand, though longer initial press can provide higher surface accuracy,long initial press time makes it impossible to shorten cycle time andsometimes badly affects on mold lifetime, and therefore it should beequal to or shorter than 60 seconds. Molding pressure may beappropriately selected considering temperatures of the glass materials,molds and the like, and it may normally be a pressure in a range of from30 to 300 kg/cm³.

After molding, the vicinity of the molding surfaces of the molds iscooled at a rate equal to or more than 20° C./minute. The cooling ratemay be smaller than 20° C./minute, but it only results in anunnecessarily long molding cycle time. Though it may vary depending onsizes and shapes of molded articles, it is preferred that the vicinityof the molding surfaces is cooled at a rate of from 20 to 180° C./minuteto obtain high surface accuracy.

After the initial press, secondary press is preferably carried out at aconstant pressure corresponding to 5 to 70% of the pressure of theinitial press and the vicinity of the molding surfaces is cooled whilemaintaining the pressure, because this may provide good surface accuracywithout sink mark and surface distortion. More preferably, the secondarypress is carried out at a pressure corresponding to 20 to 50% of thepressure used for the initial press.

Further, to obtain final products with a center thickness within theallowance, it is preferred that the heated and softened glass materialsare initially pressed so that it has a center thickness with in a rangeof from a thickness smaller than that of final products by 0.03 mm to athickness larger than the same by 0.15 mm, and then subjected to thesecondary press. Since in the secondary press the pressure is rapidlyreduced and the glass have a high viscosity, the center thickness may bechanged only by about 0.001 to 0.12 mm and hence it is easy to obtainthe center thickness within a range of the allowance ±0.03 mm.

Regarding the initial press and the secondary press described above, theinitial press is preferably stopped by a means for stopping initialpress so that the glass material has a desired center thickness, i.e., athickness within a range of from a thickness smaller than that of finalproducts by 0.03 mm to a thickness larger than the same by 0.15 mm, andthe secondary press is preferably started before the initial press isstopped or upon the stop of the initial press. Such an operation resultsin a desired center thickness and good surface accuracy because theinitial press and the secondary press are carried out with continuouspressurization. When the desired center thickness is obtained by, forexample, an external stopper, and then the secondary press is performed,it sometimes becomes difficult to obtain good surface accuracy becausethe press operation is interrupted for a moment. The initial press andthe secondary press described above are preferably carried out in adouble cylinder structure. Such a double cylinder structure will beexplained in detail in the Examples hereinafter.

The glass molded articles press molded and cooled as described above arereleased from the molds when the temperature of the vicinity of themolding surfaces becomes below a temperature at which the glass materialhas a viscosity of 10¹² poises. Glass materials having a viscosityexceeding 10¹² poises do not show viscous flow in a short period of timeand may be considered substantially solidified. Therefore, deformationand the like of the glass molded articles after the release from moldsare prevented and good surface accuracy can be obtained. It isparticularly preferred that the glass molded articles are released fromthe molds at a temperature at which the glass material has a viscosityof 10¹³ to 10^(14.5) poises.

The molds used in this process of the present invention are notparticularly limited except for the molding surfaces. Those means forheating and cooling the molds described for the first aspect of thepresent invention may also be used for this process.

The molds used for this process of the present invention may be, forexample, a mold assembly 39 comprising an upper mold 35, a lower mold 34and a guide mold 36 as shown in FIG. 16. However, molds are not limitedto it. The molds may be those composed of silicon carbide, silicon,silicon nitride, tungsten carbide or cermets of aluminum oxide-base andcermets of titanium carbide-base and such materials preferably furthercoated with diamond, heat resistant metals, noble metal alloys, ceramicsof carbides, nitrides, borides, oxides and the like. Particularlypreferred are those obtained by forming a silicon carbide layer on asilicon carbide sintered body by a CVD technique, processing it into afinished shape and forming thereon an amorphous and/or crystallinecarbon mono-component or mixture layer of graphite structure and/ordiamond structure such as i-carbon layers by an ion-plating technique orthe like. In the molds having such carbon layers as described above,adhesion of glass by fusion would not occur even if the molding iscarried out at a relatively high molding temperature and molded articlesare easily released from the molds at a relatively high temperaturebecause of good mold release property.

In this process of the present invention, like the process according tothe first aspect of the present invention, heating and softening of theglass materials can be performed while the materials are floated by agas blow and the heated and softened glass materials are transferred tothe preheated molds.

Type and flow rate of the gas for floating the glass materials by itsblow may be similar to those described for the process according to thefirst aspect of the present invention, and floating of the glassmaterials by a gas blow and transfer of the glass materials may also becarried out as described for the process according to the first aspectof the present invention by referring to FIGS. 2 to 15.

According to the present invention, in a process for manufacturing glassoptical elements by press molding a heated and softened glass materialin preheated molds, even if the glass material is likely to be deformedwhen it is softened to a low viscosity, it can be heated and softenedwhile easily holding it.

According to the present invention, glass optical elements having goodoptical properties can be manufactured by transferring a heated andsoftened glass material which is likely to be deformed to molds withoutunduly deforming it.

According the the present invention, glass optical elements can bemanufactured by using a glass material which enables to provide a moldedglass having a size approximately the same as the desired size of apurpose glass optical element after molding so that an edging volume forcentering in post-processing may be minimized.

Further according to the present invention, glass optical elementshaving few surface defects and high surface accuracy can be manufacturedwhile the cycle time required for the molding is markedly shortened.

In addition, according to the present invention, even biconvex lenses,meniscus lenses and the like with a small edge thickness can be easilymanufactured.

According to the present invention, glass optical elements having goodproperties can be manufactured by transferring a heated and softenedglass gob, which is prone to be deformed, to molds.

According to the present invention, it is possible to provide a processfor manufacturing glass optical elements without sink marks anddistortion and with high surface accuracy.

According to the present invention, it is possible to provide a processcapable of manufacturing glass optical elements without sink marks anddistortion and with high surface accuracy and a center thickness withinallowance.

That is, according to the present invention, glass optical elements withfew surface defects and high surface accuracy can be manufactured with amarkedly shortened cycle time required for the press molding whencompared with that of conventional processes by heating molds and glasspreforms together (5 to 20 minutes/cycle).

Further, the present invention provides a process capable ofmanufacturing glass optical elements while completely preventing glassadhesion to molding surfaces.

EXAMPLES

The present invention will be further explained by referring to thefollowing examples.

Example 1

Molds for Press Molding

Molds for press molding comprised, as shown in FIG. 17, a mold substratewhich was obtained by grinding a substrate material of silicon carbide(SiC) sintered body 31 into a shape of mold for press molding, forming asilicon carbide layer 32 on the molding surface portion by a CVDtechnique, grinding and polishing the surface to finish it as a mirrorsurface corresponding to the shape of glass molded articles to beproduced. A layer of i-carbon (diamond-like carbon) 33 with a thicknessof 500 Å was further formed on the silicon carbide layer 32 of the moldsubstrate by an ion plating technique to give a lower mold 34 having amolding surface 40 for manufacturing φ 18 mm biconvex glass lenses (φ 15mm after edging for centering).

An upper mold 35 shown in FIG. 1 was also obtained in a manner similarto that for obtaining the lower mold 34 described above. The upper mold35 and the lower mold 34 are disposed coaxially as shown in FIG. 1, anda mold assembly 39 was constituted by the upper mold 35 and the lowermold 34 as well as a guide mold 36 for guiding them upon press molding.

The lower mold 34 and the upper mold 35 were heated by mold heaters 44,which were provided around the outside of cylindrical molds 37 andcontrolled by a thermocouple 44 for measuring mold temperature insertedinto inside of the lower mold 34 from lower part of a mold support 38.Temperature of the cylindrical molds 37 was measured by thermocouples 43for measuring cylindrical mold temperature inserted into inside of thecylindrical molds 37.

Floating Means and Transfer Means

In a single closed chamber (not shown) including the mold heatingstructure described above, there were also provided a floating means anda transfer means shown in FIG. 2.

A glassy carbon floating means 10 (hereinafter referred to as “GCfloating means”) set on a floating means support 13 is disposed betweenglass softening heaters 14 for heating and softening a glass material(preform) 1. The glass material 1 was floated and held by a gas blow of98% N₂+2% H₂ gas at a flow rate of 100 ml/minute fed from inside of thefloating means support 13 to lower part of the GC floating means 10.

Further, outside the glass softening heaters 14, there was a glassycarbon vacuum pad 15 (hereinafter referred to as “GC vacuum pad”), whichcan move vertically and horizontally, and it was normally waiting at aposition over the GC floating means 10.

Preheating and Press Processes

The closed chamber (not shown) including the press molding structure andthe glass heating structure described above was evacuated to vacuum and98% N₂+2% H₂ gas was introduced into the chamber to form an atmosphereof the gas in the chamber.

Then, the mold assembly was heated by the mold heaters 44 until thetemperatures of the upper mold 35 and the lower mold 34 reached to 576°C. measured by the thermocouples 43 for measuring mold temperature sothat they had a temperature around the deformation point of the preform1 composed of barium borosilicate optical glass (marble-shaped hotformed article having a surface-defect-free mirror surface, weight; 1000mg, transition point; 534° C., deformation point; 576° C.) andmaintained at the same temperature. Glass viscosity at the transitionpoint is 10^(13.4) poise and that at the deformation point is 10¹⁰⁻¹¹poise.

On the other hand, the glass preform 1 floating above the GC floatingmeans 10 was heated by the glass softening heaters 14 to 700° C. wherethe glass has a viscosity of 10⁶ poises and softened.

Then, the GC vacuum pad 15, which had been kept waiting at the positionoutside the glass softening heaters 14 and over the GC floating means10, was descended to the position of the preform 1 to catch the preformby suction. At this point, the GC vacuum pad had been heated by theradiation heat from the glass softening heaters 14 and had a temperatureof from 300 to 400° C. and therefore it was not likely to react with thelow viscosity glass.

Then, the GC vacuum pad 15 holding the preform 1 was immediately movedto a position above the lower mold 34 as shown in FIG. 6 and descendedto a position near the molding surface 40 of the lower mold 34 and thesuction was stopped to place the preform 1 on the molding surface 40 ofthe lower mold 34. After that, the GC vacuum pad 15 was removed from theposition above the lower mold 34 and returned to the original waitingposition and therefore there were no obstacles above the lower mold 34.The lower mold 34 was lifted up by the mold support 38 in a moment to aposition under the upper mold 35, which was disposed coaxially with thelower mold 34 thereabove and fixed together with the mold support 38, topress mold the preform for 10 seconds at a pressure of 100 kg/cm² in themold assembly 39 comprising the upper mold 35, the lower mold 34 and theguide mold 36 guiding them so that a desired thickness was obtained.Then, the mold heaters 44 were turned off and the glass molded article 2and the mold assembly 39 were allowed to cool. Seventy seconds later,when the temperatures of the upper mold 35 and the lower mold 34measured by the thermocouples 42 for measuring mold temperature became534° C. corresponding to the glass transition point, the glass moldedarticle 2 was released and removed from the mold assembly 39.

With respect to the glass molded article 2 (outer diameter; φ 18 mm,thickness; 2.9 mm, biconvex lens) obtained as described above, afterannealing, surface accuracy was evaluated by an interferometer andsurface quality was evaluated in terms of visual appearance and by astereoscopic microscope. Results are shown in Table 1. The evaluationwas performed with respect to five lenses obtained in the same manner(the same shall apply to the following examples). As a result, it wasfound that all of the lenses had good properties.

Example 2

Though the glass floating and softening structure was changed, the samemold assembly and molding conditions as in Example 1 were used.

Inside of the closed chamber including the press molding structure andthe glass heating structure was evacuated to vacuum and 98% N₂+2% H₂ gaswas introduced into the chamber to form an atmosphere of the gas in thechamber.

Then, the mold assembly was heated by the mold heaters 44 so that theupper mold 35 and the lower mold 34 had a temperature around deformationpoint of a preform 1 (the same glass type and the same shape as inExample 1), i.e., 576° C., and maintained at the same temperature. Onthe other hand, as shown in FIG. 4, the glass preform 1 above a porousceramic floating means 17 which was disposed on a floating means support19 and between the glass softening heaters 14 was heated to 700° C.where the glass has a viscosity of 10⁶ poises and softened, while it wasfloated by N₂ gas fed from inside of the floating means support 19 tolower part of the porous ceramic floating means 17 and blown off frompores of the floating means material at a flow rate of 200 ml/minute.

Then, a GC vacuum pad (not shown), which had been kept waiting at aposition outside the glass softening heaters 14 and over the porousceramic floating means 17, was descended to catch the softened floatingpreform 1 by suction. Then, the GC vacuum pad holding the preform 1 wasimmediately moved to a position above the lower mold 34 as shown in FIG.6 and descended again to a position near the surface of the lower mold34 and the suction was stopped to place the preform 1 on the moldingsurface 40 of the lower mold 34.

After that, the GC vacuum pad 15 was moved back to the original waitingposition.

Then, the lower mold 34 was lifted up by the mold support 38 to aposition under the upper mold 35, which is disposed coaxially with thelower mold 34 thereabove, to press mold the glass material 1 for 10seconds at a pressure of 100 kg/cm in the mold assembly 39 comprisingthe upper mold 35, the lower mold 34 and the guide mold 36 guiding themso that a desired thickness was obtained. Then, the mold heaters 44 wereturned off and, seventy seconds later, when the temperatures of theupper mold 35 and the lower mold 34 became 534° C. corresponding to theglass transition point, the glass molded article 2 was released andremoved from the mold assembly 39.

Properties of the glass molded article 2 (the same shape as inExample 1) obtained as described above, after annealing, were evaluatedin the same manner as in Example 1. Results are shown in Table 1.

Example 3

Except that the glass floating and softening structure was changed,Example 1 was repeated.

Inside of the closed chamber including the press molding structure andthe glass heating structure was evacuated to vacuum and 98% N₂+2% H₂ gaswas introduced into the chamber to form an atmosphere of the gas in thechamber.

Then, the mold assembly was heated so that the upper mold 35 and thelower mold 34 had a temperature around deformation point of a preform 1(the same glass type and the same shape as in Example 1), i.e., 576° C.and maintained at that temperature.

On the other hand, the glass preform 1 was heated to 504° C. on a glassholding means 20 placed on a glass holding means support 21 betweenglass preheating heaters 22 so that the preform had a temperature lowerthan its glass transition point by 30° C. and maintained at thattemperature. At that time, since the preform 1 does not exhibitflowability at the temperature, it does not need to be floated over theglass holding means 20.

Then, the GC vacuum pad, which had been kept waiting at the positionoutside the glass preheating heaters 22 and over the glass holding means20, was descended to catch the preform 1 by suction and moved to aposition above the tungsten alloy floating means 10, which had beenpreliminarily heated at 335° C. by the glass softening heater 14 so thatit had a temperature lower than the glass transition temperature by 200°C. Then the pad was descended and simultaneously the suction was stoppedto place the preform 1 on the receiving part of the floating means 10.The GC vacuum pad 15 was kept waiting at a position over the glasssoftening heaters 14.

The glass preform 1 was floated above the floating means 10 by a blow of98% N₂+2% H₂ gas at a flow rate of 200 ml/minute, which was fed frominside of the floating means support 13 to the tungsten alloy floatingmeans 10, and heated rapidly by the glass softening heaters 14 to 700°C. where the glass has a viscosity of 10⁶ poises. During this operation,because the temperature of the tungsten alloy floating means 10 had beenmade lower than that of the glass preform 1 by 170° C. when the preform1 was placed on the floating means, the temperature of the tungstenalloy floating means 10 was always lower than the temperature of theglass even after the rapid heating. Therefore, the tungsten alloyfloating means 10 did not react with the glass.

Then, the GC vacuum pad 15, which had been kept waiting over the glasssoftening heaters 14, was descended to catch the floating softenedpreform 1 by suction and immediately moved to the position above thelower mold 34 and descended again to a position near the surface of thelower mold 34 and the suction was stopped to place the preform 1 on themolding surface 40 of the lower mold 34. After that, the GC vacuum pad15 was moved back to the original waiting position.

The lower mold 34 was lifted up by the mold support 38 to a positionunder the upper mold 35 disposed coaxially with the lower mold 34thereabove to press mold the preform 1 for 10 seconds at a pressure of100 kg/cm² in the mold assembly 39 shown FIG. 1 comprising the uppermold 35, the lower mold 34 and the guide mold 36 guiding them so that adesired thickness was obtained. Then, the mold heaters 44 were turnedoff and, seventy seconds later, when the temperatures of the upper mold35 and the lower mold 34 became 534° C. corresponding to the glasstransition point, the glass molded article 2 was released and removedfrom the mold assembly 39.

Properties of the glass molded article 2 (the same shape as inExample 1) obtained as described above, after annealing, were evaluatedin the same manner as in Example 1. Results are shown in Table 1.

Example 4

Except that the mechanism for inserting a floating softened glass intothe mold assembly was changed, Example 1 was repeated.

Inside of the closed chamber including the press molding structure andthe glass heating structure was evacuated to vacuum and 98% N₂+2% H₂ gaswas introduced into the chamber to form an atmosphere of the gas in thechamber.

Then, the mold assembly was heated so that the upper mold 35 and thelower mold 34 had a temperature around deformation point of a preform 1(the same glass type and the same shape as in Example 1), i.e., 576° C.and maintained at the same temperature. Then, as shown in FIG. 7, theglass preform 1 was floated over the GC floating means 10 set on thefloating means support 13 by a gas blow of 98% N₂+2% H₂ gas at a flowrate of 300 ml/minute, which was fed from inside of the floating meanssupport 13 to lower part of the GC floating means 10, and heated to 700°C. where the glass has a viscosity of 10⁶ poises while it was floating.Then the floating means support 13 was moved to a position such that thefloating softened preform 1 was located just below the upper mold 35.

Then, as shown in FIG. 8, the floating means support 13 was lifted up totransfer the preform 1 to a position near the surface of the upper mold35 and the preform 1 was contacted to the surface of the upper mold 35by sucking from the suction holes 45 provided on the inside wall of theguide mold 36 for guiding the upper mold 35 and the lower mold 34 atpositions corresponding to the side faces of the preform 1. Whilesucking, the flow rate of the gas blow from the floating means 10 may betemporarily increased to lift up the preform 1 so that the preform canbe more smoothly contacted to the surface of the upper mold 35.

Then, the floating means support 13 was moved from the position belowthe upper mold 35 back to the initial position for heating and softeningthe glass. Simultaneously, as shown in FIG. 9, the lower mold 34 waslifted up by the mold support 38 to a position under the upper mold 35to press mold the preform 1 for 10 seconds at a pressure of 100 kg/cm²in the mold assembly 39 comprising the upper mold 35, the lower mold 34and the guide mold 36 guiding them so that a desired thickness wasobtained. Then, the mold heaters 44 were turned off and, seventy secondslater, when the temperatures of the upper mold 35 and the lower mold 34became 534° C. corresponding to the glass transition point, the glassmolded article 2 was released and removed from the mold assembly 39.

Properties of the glass molded article 2 (the same shape as inExample 1) obtained as described above, after annealing, were evaluatedin the same manner as in Example 1. Results are shown in Table 1.

Example 5

Schematic views of the apparatus and the mold assembly used in thisexample are shown in FIGS. 10, 11 and 18. The molds for molding had thesame structure as in Example 1.

The closed chamber including the press molding structure and the glassheating structure was evacuated to vacuum and 98% N₂+2% H₂ gas wasintroduced into the chamber to form an atmosphere of the gas in thechamber.

Then, the mold assembly was heated by the mold heaters 44 until thetemperatures of the upper mold 35 and the lower mold 34 reached to 592°C. at which a glass preform 1 (marble-shaped hot molded article having asurface-defect-free mirror surface, weight; 1800 mg, transition point;534° C., deformation point; 576° C.) had a viscosity of 10¹⁰ poises andmaintained at the same temperature.

On the other hand, as shown in FIG. 10, the preform 1 having a diameterslightly larger than that of the floating means on the GC floating means10 was floated by a gas blow of 98% N₂+2% H₂ gas at a flow rate of 600ml/minute, which was fed from inside of the floating means support 13 tolower part of the GC floating means 10, and heated to 660° C. at whichthe glass had a viscosity of 10^(7.2) poises while it was floating.

Then, a GC vacuum pad 24, which had been kept waiting at the positionoutside the glass softening heaters 14 and over the GC floating means10, was descended to catch by suction a ring-like member 23 disposed atthe vicinity of the GC floating means 10 and immediately ascended again.In this operation, when the periphery of the preform 1 having a diameterslightly larger than the outer diameter of the GC floating means 10 waspushed up by the inner periphery of the ring-like member 23 and thepreform 1 was transferred with the ring-like member 23, the preform didnot deformed by itself to sag and drop from the ring-like member 23,because the transfer was performed within a short period of time.

Then, as shown in FIG. 11, the GC vacuum pad 24 holding by suction thering-like member 23 on which the preform 1 was placed was immediatelymoved to a position above the lower mold 34. After that, it wasdescended again to a position near the lower mold 34 and the suction wasstopped to place the preform 1 on the molding surface 40 of the lowermold 34 and the ring-like member 23 on the flange provided at a positionslightly lower than the molding surface, respectively. Then, the GCvacuum pad 24 was removed from the position above the lower mold 34 andthe lower mold was lifted up by the mold support 38 to a position underthe upper mold 35 disposed coaxially with the lower mold 34 thereaboveto press mold the preform 1 for 10 seconds at a pressure of 100 kg/cm²in the mold assembly 39 comprising the upper mold 35, the lower mold 34and the guide mold 36 guiding them so that a desired thickness wasobtained. Then, the mold heaters 44 were turned off and, seventy secondslater, when the temperatures of the upper mold 35 and the lower mold 34became 534° C. corresponding to the glass transition point, the glassmolded article 2 was released and removed from the mold assembly 39.

Properties of the glass molded article 2 (φ 25 mm, φ 20 mm aftercentering, biconvex lens) obtained as described above, after annealing,were evaluated in the same manner as in Example 1. Results are shown inTable 1.

TABLE 1 Mold Temperature Glass temperature Floating Gas at the beginningwhen a molded glass Example (° C.) Flow Rate of molding was releasedfrom molds Evaluation of Glass Molded Articles No. (Viscosity) (cc/min)(Viscosity) (Viscosity) Surface Accuracy Surface Quality 1 700 100 576534 ◯ ◯ (10⁶ poises) (10^(10.7) poises) (10^(13.4) poises) 2 700 200 576534 ◯ ◯ (10⁶ poises) (10^(10.7) poises) (10^(13.4) poises) 3 700 200 576534 ◯ ◯ (10⁶ poises) (10^(10.7) poises) (10^(13.4) poises) 4 700 300 576534 ◯ ◯ (10⁶ poises) (10^(10.7) poises) (10^(13.4) poises) 5 660 600 590534 ◯ ◯   (10^(7.2) poises) (10¹⁰ poises)   (10^(13.4) poises)

Example 6

Glass molded articles were manufactured in the same manner as in Example1 except that kinds of preform (glass types and shapes), floating gasflow rates and mold release temperatures indicated in Table 2 were used.Properties of the obtained glass molded articles were evaluated in thesame manner as in Example 1. Results are shown in Table 2. All of theglass molded articles exhibited good properties.

TABLE 2 Glass Article Floating Gas Mold Temperature Mold ReleaseTemperature Flow Rate (° C.) Temperature (° C.) Evaluation of GlassMolded Articles (Viscosity) Shape (cc/min) (Viscosity) (Viscosity)Surface Precision Surface Condition 683° C. Hot Formed 300 576° C. 549°C. ◯ ◯ (10^(6.5) poises) Article 600 (10^(10.7) poises) (10^(12.3)poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) Polished 200 ◯ ◯ Sphere 400 ◯ ◯ 700° C. Hot Formed 300 568° C.534° C. ◯ ◯ (10⁶ poises)   Article 600 (10^(11.2) poises) (10^(13.4)poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) Polished 200 ◯ ◯ Sphere 400 ◯ ◯ 718° C. Hot Formed 300 557° C.525° C. ◯ ◯ (10^(5.5) poises) Article 600 (10^(11.7) poises) (10¹⁴poises)   ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) P Polished 200 ◯ ◯ Sphere 400 ◯ ◯

Example 7

Mold Assembly for Press Molding

The same mold assembly as in Example 1 was used.

Floating Means

In a single closed chamber (not shown) including the mold heatingstructure described above, there were provided floating means 10 (10 a,10 b), guide means 50 (50 a, 50 b) shown in FIG. 12 and the glasssoftening heaters 13 for heating and softening glass materials. Thefloating means 10 was a split floating means composed of glassy carbon(hereinafter referred to “GC split floating means”) and the guide means50 was a split cylindrical guide composed of the same material(hereinafter referred to as “GC split cylindrical guide”). The glassmaterial 1 was floated by a gas blow of 98% N₂+2% H₂ gas at a flow rateof 200 to 600 ml/minute supplied from inside of the GC split floatingmeans.

Heating for Softening and Pressing Processes

The closed chamber including the press molding structure and the glassheating structure described above was evacuated to vacuum and 98% N₂+2%H₂ gas was introduced into the chamber to form an atmosphere of the samegas in the chamber.

Then, the mold assembly was heated by the mold heaters 44 shown in FIG.19 until the temperatures of the upper mold 35 and the lower mold 34reached to 576° C., 565° C. or 557° C. measured by the thermocouples 43for measuring mold temperature so that they had a temperature around thedeformation point of a glass preform 1 identical to that of Example 1and maintained at the same temperature (Table 3). In this operation, theupper mold and the lower mold were separately heated at differentpositions and assembled together as an integrated mold assembly as shownin FIG. 19 upon molding.

On the other hand, the glass material 1 (preform) above the GC splitfloating means 10 was heated by the glass softening heaters 13 to 683°C., 700° C. or 718° C. where the glass has a viscosity of 10^(4.5) to10^(5.5) poises and maintained at the same temperatures.

Then, the GC split floating means 10 holding the floating heated andsoftened glass material 1 was immediately moved to the position justabove the lower mold 34 and, as shown in FIG. 13, the GC split floatingmeans 10 a and the GC split floating means 10 b were moved in horizontaldirection to right and left in a moment to make an opening and drop theglass material 1 onto the molding surface 40 of the lower mold 34. TheGC split cylindrical guide 50 having an inner diameter allowing anappropriate clearance against the maximum outer diameter of the glassmaterial 1 was provided just above the GC split floating means 10. Whenthe GC split floating means was opened and the glass material wasdropped, the GC split cylindrical guide 50 served as a guide whichminimize the setting deviation of the glass material 1 on the lower mold34.

After the glass was dropped, the GC split cylindrical guides 50 a and 50b were horizontally moved in opposite directions, right and left, tomake an opening. Therefore, there are no obstacles above the lower mold34 and the mold support 38 lifted up the lower mold in a moment to aposition under the upper mold 35, which was disposed coaxially with thelower mold 34 thereabove and fixed together with the mold support 38, topress mold the glass material 1 for 10 seconds at a pressure of 100kg/cm² in the mold assembly comprising the upper mold 35, the lower mold34 and the guide mold 36 guiding them so that a desired thickness wasobtained as shown in FIG. 19. Then, the mold heaters 44 were turned offand the glass molded article 2 and the mold assembly were allowed tocool. Seventy seconds later, when the temperatures of the upper mold 35and the lower mold 34 measured by the thermocouples 43 for measuringmold temperature became 549° C., 534° C. or 525° C., the glass moldedarticle 2 was released and removed from the mold assembly.

With respect to the glass molded articles 2 (outer diameter; φ 18 mm,thickness; 2.9 mm, biconvex lens) obtained as described above, afterannealing, surface accuracy was evaluated by an interferometer andsurface quality was evaluated in terms of visual appearance and by astereoscopic microscope. Results are shown in Table 3.

In Table 3, shown are results of evaluation of glass molded articlesobtained by varying temperature of the softened glass material 1, shapeof the glass material 1, gas flow rate from the GC split floating means,mold temperature and mold release temperature. As a result, it was foundthat all of the molded articles (lenses) had good properties.

TABLE 3 Glass Article Floating Gas Mold Temperature Mold ReleaseTemperature Flow Rate (° C.) Temperature (° C.) Evaluation of GlassMolded Articles (Viscosity) Shape (cc/min) (Viscosity) (Viscosity)Surface Precision Surface Condition 683° C. Hot Formed 300 576° C. 549°C. ◯ ◯ (10^(6.5) poises) Article 600 (10^(10.7) poises) (10^(12.3)poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) Polished 200 ◯ ◯ Sphere 400 ◯ ◯ 700° C. Hot Formed 300 568° C.534° C. ◯ ◯ (10⁶ poises)   Article 600 (10^(11.2) poises) (10^(13.4)poises) ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) Polished 200 ◯ ◯ Sphere 400 ◯ ◯ 718° C. Hot Formed 300 557° C.525° C. ◯ ◯ (10^(5.5) poises) Article 600 (10^(11.7) poises) (10¹⁴poises)   ◯ ◯ Ground Spherical 300 ◯ ◯ Surface Article 600 ◯ ◯ (#800diamond) P Polished 200 ◯ ◯ Sphere 400 ◯ ◯

Examples 8-1 to 8-5

Mold Assembly for Press Molding

A mold assembly shown in FIG. 16 provided with the same molds as inExample 1 was used.

Floating Means and Transfer Means

In a single closed chamber (not shown) including the mold heatingstructure described above, there were also provided the floating meansand the transfer means shown in FIG. 2.

Glass softening heaters 14 for heating and softening glass materials(preform) 1 were also provided and a glassy carbon floating means 10(hereinafter referred to “GC floating means”) set on a floating meanssupport 13 was provided between the glass softening heaters 14. Theglass material 1 was floated by a gas blow of 98% N₂+2% H₂ gas (Examples8-1 to 8-3) or N₂ gas (Examples 8-4 and 8-5) at a flow rate indicated inTable 4 fed from inside of the floating means support 13 to lower partof the GC floating means 10.

Further, outside the glass softening heaters 14, there was a glassycarbon vacuum pad 15 (hereinafter referred to as “GC vacuum pad”), whichcan move vertically and horizontally, and it was normally waiting at aposition over the GC floating means 10.

Heating for Softening and Pressing Processes

The closed chamber (not shown) including the press molding structure andthe glass heating structure described above was evacuated to vacuum and98% N₂+2% H₂ gas was introduced into the chamber to form an atmosphereof the same gas in the chamber.

The process will be exemplified below by utilizing a preform 1 composedof barium borosilicate optical glass (marble-shaped hot formed articlehaving a surface-defect-free mirror surface, weight; 1000 mg, transitionpoint; 534° C., deformation point; 576° C.). The mold assembly washeated by the mold heaters 44 until the temperatures of the upper mold35 and the lower mold 34 (mold temperature) measured by thethermocouples 43 for measuring mold temperature had reached to atemperature indicated in Table 4 at which the preform had a viscosityalso indicated in Table 4 and maintained at the same temperature. A partof relation between glass viscosity and its temperature was shown below.

Glass Viscosity Temperature 10⁹ poises 614° C. 10¹⁰ poises 592° C. 10¹¹poises 572° C. 10¹² poises 554° C. 10^(12.7) poises 543° C. 10^(13.4)poises 534° C. 10^(14.5) poises 518° C.

On the other hand, the glass preform 1 above the GC floating means 10was heated by the glass softening heaters 14 to a temperature indicatedin Table 4 corresponding to a viscosity also indicated in Table 4 tosoften it while it was floated. Further relation between glass viscosityand its temperature was shown below.

Glass Viscosity Temperature 10^(5.5) poises 718° C. 10^(6.4) poises 686°C. 10^(7.3) poises 658° C. 10^(8.2) poises 634° C. 10^(8.8) poises 619°C.

Then, the GC vacuum pad 15, which had been kept waiting at a positionoutside the glass softening heaters 14 and over the GC floating means10, was descended to the position of the preform 1 to catch the preform1 by suction. At this point, the GC vacuum pad had been heated by theradiation heat from the glass softening heaters 14 and had a temperatureof 300 to 400° C. and therefore it did not react with the low viscosityglass.

Then, as shown in FIG. 6, the GC vacuum pad 15 holding the preform 1 wasimmediately moved to the position above the lower mold 34 and descendedagain to a position near the molding surface 40 of the lower mold 34 andthe suction was stopped to place the preform 1 on the molding surface 40of the lower mold 34. After that, the GC vacuum pad 15 was moved fromthe position above the lower mold 34 back to the original waitingposition and therefore there are no obstacles above the lower mold 34.The mold support 38 lifted up the lower mold in a moment to a positionunder the upper mold 35, which was disposed coaxially with the lowermold 34 thereabove and fixed together with the mold support 38, to pressmold the preform 1 for 10 seconds at a pressure of 100 kg/cm² in themold assembly 39 comprising the upper mold 35, the lower mold 34 and theguide mold 36 guiding them. In this molding process, the lower end ofthe guide mold 36 was stopped by a flange of the lower mold 34 to give athickness of the molded article larger than that of final product by 30μm. On the other hand, five seconds after the start of the pressing withthe first cylinder, a pressure of 20 kg/cm² (Examples 8-1 to 8-5) wasapplied to the back side of the upper mold 35 by a pushing bar 45connected to the second cylinder which was provided inside the firstcylinder to pressurize and hold the glass molded article 2 and the moldassembly 39. Then, the mold heaters 44 were turned off and the glassmolded article 2 and the mold assembly 39 were allowed to cool. After aperiod of time indicated in Table 4 as molding time (initial press time[10 seconds]+secondary press time) was passed, mold temperatures of theupper mold 35 and the lower mold 34 measured by the thermocouples 42 formeasuring mold temperature reached to a temperature indicated in Table 4as mold release temperature and a desired thickness of the glass moldedarticle was obtained, the glass molded article 2 was released andremoved from the mold assembly 39. Relation between glass viscosity andits temperature was shown above.

With respect to the glass molded articles 2 (biconvex lenses having anouter diameter; φ 18 mm, thickness; 2.9 mm, and edge thickness; 1.0 mm)obtained as described above, after annealing, surface accuracy wasevaluated by an interferometer and surface quality was evaluated interms of visual appearance and by a stereoscopic microscope. Results areshown in Table 4 as Examples 8-1 to 8-5. As a result, it was found thatall of the lenses had good properties.

Examples 9-1 to 9-5

Mold Assembly for Press Molding

The used mold assembly for press molding was the same as in Example 7except that it did not have the pushing bar 45.

Floating Means

In a single closed chamber (not shown) including the mold heatingstructure described above, there were provided the floating means 10 (10a, 10 b), the guide means 50 (50 a, 50 b) shown in FIG. 12 and the glasssoftening heaters (not shown). The floating means 10 was a splitfloating means composed of glassy carbon (hereinafter referred to “GCsplit floating means”) and the guide means 50 was a split cylindricalguide composed of the same material (hereinafter referred to as “GCsplit cylindrical guide”). The glass material 1 was floated by a gasblow of 98% N₂+2% H₂ gas at a flow rate indicated in Table 4 suppliedfrom inside of the GC split floating means.

Heating for Softening and Pressing Processes

The closed chamber including the press molding structure and the glassheating structure described above was evacuated to vacuum and 98% N₂+2%H₂ gas was introduced into the chamber to form an atmosphere of the samegas in the chamber.

Then, the mold assembly was heated by the mold heaters 44 shown in FIG.19 until the temperatures of the upper mold 35 and the lower mold 34reached to 572° C. (Examples 9-1 to 9-3 and 9-5) or 554° C. (Example9-4) measured by the thermocouples 43 for measuring mold temperature atwhich temperatures the same glass material as in Example 8 shows aviscosity of 10¹¹ or 10¹² poises, respectively, and maintained at thesame temperature. In this operation, the upper mold and the lower moldwere separately heated at different positions and assembled together asan integrated mold assembly as shown in FIG. 19 upon molding.

On the other hand, the glass material 1 above the GC split floatingmeans 10 was heated by the glass softening heaters to 718° C. where theglass had a viscosity of 10^(5.5) poises as indicated in Table 4 andmaintained at the same temperature.

Then, the GC split floating means 10 holding the floating glass material1 was immediately moved to a position just above the lower mold 34 and,as shown in FIG. 13, the GC split floating means 10 a and the GC splitfloating means 10 b were splitted and moved horizontally in oppositedirections, right and left, in a moment to make an opening and therebydrop the glass material 1 onto the molding surface 40 of the lower mold34. The GC split cylindrical guide 50 having an inner diameter allowingan appropriate clearance against the maximum outer diameter of the glassmaterial 1 was provided just above the GC split floating means 10. Whenthe GC split floating means 10 was opened and the glass material 1 wasdropped, the GC split cylindrical guide 50 served as a guide whichminimizes the setting deviation of the glass material 1 on the lowermold 34.

After the glass was dropped, the GC split cylindrical guides 50 a and 50b were horizontally moved in opposite directions, right and left, tomake an opening. Therefore, there are no obstacles above the lower mold34 and the mold support 38 lifted up the lower mold 34 in a moment tothe upper mold 35, which was disposed coaxially with the lower mold 34thereabove and fixed together with the mold support 38, to press moldthe glass material 1 for 10 seconds at a pressure of 100 kg/cm² in themold assembly comprising the upper mold 35, the lower mold 34 and theguide mold 36 guiding them so that a desired thickness was obtained andthe pressure was changed to 50 kg/cm² in a moment. Then, the moldheaters 44 were turned off and the glass molded article 2 and the moldassembly were allowed to cool. After a period of time indicated in Table4 as molding time (initial press time [10 seconds]+secondary press time)was passed and the temperatures of the upper mold 35 and the lower mold34 measured by the thermocouples 43 for measuring mold temperaturereached to a temperature indicated in Table 4 as mold releasetemperature, the glass molded article 2 was released and removed fromthe mold assembly

With respect to the glass molded articles 2 (biconvex lenses having anouter diameter; φ 18 mm, thickness; 2.9 mm and edge thickness; 1.0 mm)obtained as described above, after annealing, surface accuracy wasevaluated by an interferometer and surface quality was evaluated interms of visual appearance and by a stereoscopic microscope. Results areshown in Table 4.

In Table 4, shown are results of evaluation of glass molded articlesobtained by varying temperature of the softened glass material 1, shapeof the glass material 1, gas flow rate from the GC split floating means,mold temperature and mold release temperature. As a result, it was foundthat all of the molded articles (lenses) had good properties.

Examples 10-1 to 10-3

Glass molded articles (biconvex lenses having an outer diameter; φ 18mm, thickness; 2.9 mm and edge thickness; 1.0 mm) were obtained in thesame manner as in Example 8-1 except that the initial press time was 5seconds (Example 10-1), 30 seconds (Example 10-2) or 55 seconds (Example10-3). With respect to the glass molded articles after annealing,surface accuracy was evaluated by an interferometer and surface qualitywas evaluated in terms of visual appearance and by a stereoscopicmicroscope. Results are shown in Table 4.

Examples 11-1 and 11-2

Glass molded articles (biconvex lenses having an outer diameter; φ 18mm, thickness; 2.9 mm and edge thickness; 1.0 mm) were obtained in thesame manner as in Example 8-1 except that the mold assembly was allowedto start to cool at the start of the initial press (pressed with apressure of 100 kg/cm²) (Example 11-1) or five second after the start ofthe initial press (Example 11-2).

With respect to the glass molded articles after annealing, surfaceaccuracy was evaluated by an interferometer and surface quality wasevaluated in terms of visual appearance and by a stereoscopicmicroscope. Results are shown in Table 4.

TABLE 4 Mold Temperature Glass Floating at Start Molding PressureCooling Mold Temperature Evaluation of Temperature Gas Flow of Molding(kg/cm²) Molding Rate at Mold Release Glass Molded Articles (° C.) Rate(° C.) Initial Secondary Time (° C./ (° C.) Surface Surface Example No.(Viscosity) (1/min) (Viscosity) Press Press (sec) min) (Viscosity)Precision Condition 8-1 686° C. 0.5 592° C. 100 20 85 47 534° C. ⊚ ⊚(10^(6.4) poises) (10¹⁰ poises) (10^(13.4) poises) 8-2 686° C. 0.5 572°C. 100 20 70 26 546° C. ⊚ ⊚ (10^(6.4) poises) (10¹¹ poises) (10^(12.5)poises) 8-3 658° C. 1.0 614° C. 100 20 85 65 534° C. ⊚ ⊚ (10^(7.3)poises) (10⁹ poises)  (10^(13.4) poises) 8-4 658° C. 1.0 592° C. 100 2050 57 554° C. ◯ ⊚ (10^(7.3) poises) (10¹⁰ poises) (10^(12.0) poises) 8-5620° C. 1.0 610° C. 100 20 90 64 525° C. ⊚ ⊚ (10^(8.8) poises) (10^(9.2)poises)  (10^(14.0) poises) 9-1 718° C. 0.5 572° C. 100 50 70 29 543° C.⊚ ⊚ (10^(5.5) poises) (10¹¹ poises) (10^(12.7) poises) 9-2 718° C. 0.5572° C. 100 50 70 43 529° C. ⊚ ⊚ (10^(5.5) poises) (10¹¹ poises)(10^(13.7) poises) 9-3 718° C. 0.5 572° C. 100 50 85 45 516° C. ◯ ⊚(10^(5.5) poises) (10¹¹ poises) (10^(14.7) poises) 9-4 718° C. 0.5 554°C. 100 50 70 21 534° C. ⊚ ⊚ (10^(5.5) poises) (10¹² poises) (10^(13.4)poises) 9-5 718° C. 0.5 572° C. 100 20 82 45 518° C. ⊚ ⊚ (10^(5.5)poises) (10¹¹ poises) (10^(14.5) poises) 10-1  686° C. 0.5 592° C. 10020 80 47 534° C. ⊚ ⊚ (10^(6.4) poises) (10¹⁰ poises) (10^(13.4) poises)10-2  686° C. 0.5 592° C. 100 20 105 47 534° C. ⊚ ⊚ (10^(6.4) poises)(10¹⁰ poises) (10^(13.4) poises) 10-3  686° C. 0.5 592° C. 100 20 130 47534° C. ⊚ ⊚ (10^(6.4) poises) (10¹⁰ poises) (10^(13.4) poises) 11-1 686° C. 0.5 592° C. 100 20 75 47 534° C. ⊚ ⊚ (10^(6.4) poises) (10¹⁰poises) (10^(3.4) poises) 11-2  686° C. 0.5 592° C. 100 20 80 47 534° C.⊚ ⊚ (10^(6.4) poises) (10¹⁰ poises) (10^(13.4) poises)

The symbols used in the evaluation of the glass molded articles have thefollowing meanings.

Surface Accuracy

∘: not more than 0.5 fringes of irregularity

⊚: not more than 0.2 fringes of irregularity

Surface Quality

⊚: good

In the above examples of the present invention, used were the moldsobtained by forming a silicon carbide layer on a silicon carbidesintered body by a CVD technique and forming thereon an i-carbon layerby an ion-plating technique. However, in addition to such molds, it wasfound that those composed of silicon, silicon nitride, tungsten carbideor cermets of aluminum oxide-base and cermets of titanium carbide-baseand such materials further coated with diamond, heat resistant metals,noble metal alloys, ceramics of carbides, nitrides, borides, oxides andthe like may be used. However, the i-carbon layer was particularlypreferred since it showed good mold release property.

In the above Examples 8 to 11, the cycle time was a sum of molding timeand recovery time of mold temperature (time required for elevating amold temperature at mold release to a temperature required for startingthe molding). Since the molds were heated by resistance heating in thoseexamples, the recovery time was about 35 seconds. Therefore, the cycletime was about 85 to 165 seconds.

The recovery time may be shortened to about 10 seconds by performing theheating of the molds with high-frequency heating or infrared heating,and hence the cycle time may be shortened as much as the time shortenedby the heating means.

What is claimed is:
 1. Method for manufacturing a glass optical elementby press molding a preheated glass material in preheated molds, whichcomprises the steps of: a. preheating the glass material and the moldsso that the temperature of the glass material is higher than thetemperature of the molds; b. transferring the preheated glass materialto the preheated molds; c. pressing the transferred glass material inthe preheated molds to form a molded glass article; d. cooling themolded glass article; and e. removing the molded glass article from themolds, wherein the pressing in step c comprises an initial press and asecondary press, the secondary press being of lower pressure than theinitial press.
 2. The method of claim 1, wherein the glass material ispreheated to a temperature at which the glass material has a viscosityof lower than 10⁹ poises, and the molds are preheated to a temperatureat which the glass material has a viscosity of from 10⁹ to 10¹² poises.3. The method of claim 2, wherein the glass material is preheated to atemperature at which the glass material has a viscosity equal to orlower than 10^(8.8) poises, and the molds are preheated to a temperatureat which the glass material has a viscosity of from 10⁹ to 10¹² poises.4. The method of claim 2, wherein the removing in step e is carried outwhen the temperature of the molds is equal to or lower than atemperature at which the glass material has a viscosity of 10¹² poises.5. The method of claim 2, wherein the glass material is preheated to atemperature at which the glass material has a viscosity of lower than10⁹ poises, and the molds are preheated to a temperature at which theglass material has a viscosity of from 10⁹ to 10¹² poises wherein thedifference between the glass material and the molds ranges from 10° to164° C.
 6. The method of claim 1, wherein the secondary press is carriedout at a pressure corresponding to 5 to 70% of the pressure of theinitial press.
 7. The method of claim 1, wherein the preheating of theglass material is carried out while the glass material is floated by agas.
 8. A process for manufacturing a glass optical element by pressmolding a preheated glass material in preheated molds, which comprisesthe steps of: f. preheating the glass material and the molds so that thetemperature of the glass material is higher than the temperature of themolds; g. transferring the heated glass material to the preheated molds;h. pressing the transferred glass material in the preheated molds toform a molded glass article; i. cooling the molded glass article; and j.removing the molded glass article from the molds, wherein the cooling instep i is started at the time when the pressing is started or during thetime the pressing is carried out.
 9. The process of claim 8, wherein thecooling is carried out at a rate of at least 20° C./minutes.
 10. Theprocess of claim 9, wherein the cooling is carried out until the moldsreach a temperature at which the glass material has a viscosity of 10¹²poises.
 11. The process of claim 8, wherein the glass material ispreheated to a temperature at which the glass material has a viscosityequal to or lower than 10^(8.8) poises, and the molds are preheated to atemperature at which the glass material has a viscosity of from 10⁹ to10¹² poises.
 12. The process of claim 8, wherein the glass material ispreheated to a temperature at which the glass material has a viscosityof lower than 10⁹ poises, and the molds are preheated to a temperatureat which the glass material has a viscosity of from 10⁹ to 10¹² poiseswherein the difference between the glass material and the molds rangesfrom 10° to 164° C.
 13. The process of claim 8, wherein the pressing instep h comprises an initial press and a secondary press, the secondarypress being of lower pressure than the initial press.
 14. The process ofclaim 13, wherein the secondary press is carried out at a pressurecorresponding to 5 to 70% of the pressure of the initial press.
 15. Theprocess of claim 8, wherein the preheating of the glass material iscarried out while the glass material is floated by a gas.
 16. Theprocess of claim 8, wherein the removing in step j is carried out whenthe temperature of the molds is equal to or lower than a temperature atwhich the glass material has a viscosity of 10¹² poises.
 17. The processof claim 1, wherein the molds are preheated to the temperature at whichthe glass material has a viscosity of from 10⁹ to 10¹² poises.
 18. Theprocess of claim 1, wherein the glass material is preheated to thetemperature at which the glass material has a viscosity of lower than10⁹ poises.
 19. The process of claim 8, wherein the molds are preheatedto the temperature at which the glass material has a viscosity of from10⁹ to 10¹² poises.
 20. The process of claim 8, wherein the glassmaterial is preheated to the temperature at which the glass material hasa viscosity of lower than 10⁹ poises.